“Central air” has become a widely desired mode of heating, ventilation, and air-conditioning. To provide central air, an HVAC (heating-ventilation-air-conditioning) unit is installed into a house or other building. HVAC unit installations typically are designed to handle the largest expected heating or cooling/conditioning load throughout a yearly temperature cycle. Thus, for a large part of any year in any given installation, the installed HVAC unit is over-rated for the actual required heating or cooling load.
Referring to FIG. 1, a conventional HVAC unit 2 installed into a building 4 includes a compressor 6, a condenser 8, an expansion valve 10, and an evaporator 12, arranged within a housing 14 to provide a vapor-compression refrigeration system for heating, cooling, and/or conditioning the air. The conventional HVAC unit also includes a blower 16 disposed to ventilate air from an inlet 18 of the housing across either of the condenser and the evaporator for heating, cooling, and/or conditioning the air, as well known in the art. Those of ordinary skill will appreciate that other modes of air conditioning system also can be used within the HVAC unit, for example evaporative or absorption systems, and that with the refrigeration system secured the HVAC unit can be used as a ventilation unit. The housing also includes an outlet 20 to which ductwork or a plenum 22 can be attached for conveying conditioned air from the HVAC unit throughout the building. Typically, the HVAC unit includes a motor control board 24 for regulating operation of the blower and of the compressor according to the quantity of conditioned air required in the building. As discussed above, the blower and the compressor typically are over-rated, that is, the HVAC unit only needs to run part time at full capacity in order to handle the typical heating or cooling load of the building.
Referring to FIG. 2, the motor control board 24 typically includes one or more relays 26 for selectively providing electric current to the motors of the compressor and the blower, input jacks 28 for receiving sensor data and control signals, a processor 30, and one or more data storage structures 31 (such as, by way of example, PROM, EEPROM, or flash memory chips or capacitors) for storing data and/or control signals. The processor is electrically connected to the relays and to the input jacks for controlling the relays based on data and signals received from the input jacks or from the data storage structure(s).
Conventionally, the processor 30 on the motor control board 24 is configured to cycle the relays 26 on or off based on the sensor data and control signals, according to well-known algorithms for cyclic control of HVAC equipment. In some HVAC units, the relays are configured as pulse-width-modulation (PWM) circuits, and the processor can be configured to control the blower 16 and/or the compressor 6 by modulating electric voltage and/or current provided to the motors of the compressor and the blower according to other well-known algorithms. Two goals of cyclic or modulated blower and compressor control are to enhance the comfort of building occupants while minimizing consumption of electric current by the HVAC unit 2.
Regulating operation of the HVAC unit 2 by cycling electric current to the blower motor and the compressor motor results in intermittent, start-and-stop transient type operation. Mechanical, electrical, and thermal transients during startup and shutdown are major factors in determining the operative lifetime of an HVAC unit. Additionally, startup and shutdown are the noisiest phases of operation for a typical HVAC unit. Thus, for a large part of any given year, an installed HVAC unit controlled by cycling electric current will present undesirable noise.
Regulating operation of the HVAC unit 2 by modulating electric voltage and/or current to the blower motor and/or the compressor motor results in operating the motors at less than optimal efficiencies, causing undesirable consumption of electrical power and generation of waste heat.
Accordingly, it is desirable to regulate electric power consumption of the HVAC unit to match actual heating or cooling loads, without causing unduly noisy operation or adversely affecting the electrical efficiency of the HVAC unit.